UN1 Gearbox Oil Cooling

Could someone give me some guidence/advice on oil cooling a UN1 transaxle with Quaife ATB diff. Sorry, it is an Esprit not a GT40. Car is producing close to 400 hp, after 3000 miles the the SYN 5 gear oil turned to smelly yougurt and I now have gearbox whine under load when new Castrol TAF-X was put in.

One worry is that the box was not built up right in the first place, backlish not set or bearings too tight ? any thoughts on that one ? SYN 5 is supposed to me very heat resistant, but I thought i shoudl expore oil cooled to give some help to the box. It has not been opened up yet for inspection, more money....


Howard Jones

What do you do with car? Track work? How many laps in a row? Road work? How hard do you drive?

My GTD has about 370ish HP and the headers are inches above the gearbox. Very hot in the engine room! No track work YET many hours at 80mph on freeway, lots of hard low speed,<100mph, canyon runs. Redline MT90 3500 miles looks VERY good. Still red and smells the same as unused oil.

I would also be interested in a "how to" discussion on how others have plumed their Renaults for a external pump and cooler. What flow rate pump? How big a cooler? Did you use a small external oil tank to increase oil volume? How about a theromstat?

I am guessing that you would draw oil from the drain and put it back into the box thru the fill port.

How about spray jets on the diff area and the 5th gear location. Any ideas on location of spray jets? How do you meter flow thru jets?

I had same questions in order to install a cooler for gearbox .

Considering majority of usage for 'high speed road' and less usage for 'track only' I decided not (yet) to invest in such a gearbox cooler system as I am not convinced that 'high speed road usage' is justifying to go for it.
However you are welcome to convince me to do it....
As another forum member pointed out (sorry cannot recall who) - if you have more power available than traction and especially if an LSD is being used - oil temps can get too high to cope with the transmission loading. He added taking the ATB diff out would probably sort the problem and I suspect he's spot on - he added it would also make us slower too though. /ubbthreads/images/graemlins/frown.gif which I'm sure it would.

We have an external oil pump that scavenges from the sump plug location, it is filtered, cooled and fed back into box above 5th gear and also to diff area. The diff gets the lions share of the returned oil as that is where our specific problems have been occuring. We also have a temp guage fitted now so will monitor what is going on in future.

I'll post pics when I get a chance to take/find them.

Almost forgot - box is UN1 with Derek Bell/Quaife Primary input shaft with longer 1st/2nd and 3.44 final + Quaife ATB and runs Silkolene Syntran Syn5.

Howard Jones

Paul I was thinking about increasing oil volume, 1 more quart, by adding a small tank. Draw from bottom of gearbox via AN6 line, thru pump, cooler, then to sealed tank then still under pressure to gearbox return.

Did you weld bungs to gearbox or simply drill and tap casting?

Do we need additional oil volume?

What kind of pump?

Fine screen rebuildable filter right?
Hi Howard

We drilled and tapped the castings, fitting M10 to -6 fittings or 1/8NPT to -6 as required. Positions were chosen to give enough metal for thread to bite. On top of box (over diff) + top of 5th gear cover. Used Dowty washers to seal fitting to box. The lower fittings would be best fitted to welded bungs, but we araldited in place to seal anyway.

Additional oil was added to system to maintain a good 'dipping depth' for the crownwheel and to allow for the additional capacity of pipework, pump, filter, cooler etc. We also assumed the oil would take a small period to travel from 5th to diff area so did'nt want to starve the cw.

I'll post details of the pump once I look it up - it came from Think Automotive I believe.

Yes - the oil passes through a thin screen in line filter that can be disassembled for cleaning and 'debris checking'. /ubbthreads/images/graemlins/blush.gif

Temp sensor is located in differential housing area and we would try to allow oil to warm - before engaging pump.

Paul, have you some pics of this transformation?

i had the same idea this WE after my tarck day at le Mas du Clos in france....

Hi Olivier -
A few pics - sorry for clarity - were taken a bit quick at weekend...(after Roy's off at airfield - hence dirty car!)

Pump shown on lower rear tray.


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Olivier, Paul, how did it pan out? Any further observations/tips?
Anyone else tried it?

P.S. IMO, spray nozzles should have bungs welded into the casing. Plain holes introduce stress points, since cracking is possible.
I have picked up oil from the bottom edge of the case and will pump it directly via a cooler into the input and output shafts, then also through a light relief valve T-pieced back to the top of the ATB diff center.